Edward Witten of the Institute for Advanced Study in Princeton, New Jersey, names the 11-dimensional M-Theory, which includes the five string theories known so far as a special case; M-theory includes 1-dimensional strings, 2-dimensional membranes, and 3- or more-dimensional branes; the special cases are Type-I (10-dimensional), Type-IIB (10-dimensional), Type-IIA (10-dimensional), Heterotic E (26- and 10-dimensional); Super-Gravity (11-dimensional); Heterotic O (26- and 10-dimensional).
